Lower Limb Dieback in Almond Relative to Light, Soil Moisture and

49 Pages·2010·24.23 MB·English

LLoowweerr LLiimmbb DDiieebbaacckk iinn AAllmmoonndd
RReellaattiivvee ttoo LLiigghhtt,, SSooiill MMooiissttuurree aanndd
SStteemm WWaatteerr PPootteennttiiaall
•• BBrruuccee LLaammppiinneenn
•• JJiimm AAddaasskkaavveegg
•• GGrreegg BBrroowwnnee
•• JJooee CCoonnnneellll
•• RRooggeerr DDuunnccaann
•• BBrreenntt HHoollttzz
•• TThheemmiiss MMiicchhaaiilliiddeess
•• SSaamm MMeettccaallff
Usually beginning in late April to early May, leaves
on lower limbs begin to yellow and then turn brown
Eventually, the whole limb collapses
This is different from the normal pattern of shading
related dieback- more commonly individual spurs
yellow and following year will be dead
•Data collected in 2004 and 2005 in Stanislaus
County suggested LLDB was not caused by:
• anthracnose
• Alternaria
• brown rot
• hull rot
•Isolations in 2004, 2005 and 2006 from affected
limbs showed a Phomopsis sp. and
Botryosphaeria dothidea.
Fungicide Trial #1- Duncan
• Captan or Pristine, with and without a bark penetrating
surfactant, was applied to lower canopy in Orchard #1 in
early May prior to expected onset of limb dieback
• Overall incidence of limb dieback was low
• No difference among treatments.
Fungicide Trial #2- Duncan
Materials applied to trunks and scaffolds on June 22, 2007
Symptoms rated August 17, 2007
Treatment LLDB Symptoms
(Rating 0-4)
Agri-fos @ 1.5 qt. / gal. 3.6 a
solution + 3 oz penetrant
Captan 80 WDG @ 5.66 lb 2.3 b
+ 3 oz penetrant
Untreated 2.0 b
Pristine @ 14.5 oz 1.6 b
+ 3 oz penetrant
2008 isolations- both Botryosphaeria and Phomopsis were
isolated from healthy and LLDB affected limbs
•Frequency of fungal isolations increased with time during
growing season
•More Botryosphaeria than Phomopsis were isolated in
2008
•2009 isolations- both Botryosphaeria and Phomopsis were
again isolated from both healthy and LLDB affected limbs
•More Phompsis than Botryosphaeria were isolated in 2009
(opposite situation in 2008)
•Frequency of isolation of these fungi varied by year
“The results suggest that the frequency of isolation of these
fungi depends on the year and this is another reason why the
results thus far suggest that these fungi are not directly
involved in LLDB” Themis Michailides- Almond Board Report
2009
Soil and physiological measurements to assess role
of stress in LLDB
•Midday canopy light interception
•Midday stem water potential
•Soil moisture tension